This invention pertains to fluid delivery systems and, more particularly, a system for delivery of fuel from a tank to an aircraft engine.
A known fuel delivery system for an aircraft engine has a main engine fuel pump of the positive displacement type which delivers fuel to the engine and a tank-mounted power-driven fuel boost pump which supplies fuel to the positive displacement pump. Such a system has disadvantages in those instances where the tank-mounted fuel boost pump is electrically driven, since there can be a fire hazard resulting from a crash landing since the boost pump could continue to pump fuel in the emergency situation. In military applications, such as in helicopters, there can be a problem when small arms fire, for example, penetrates the fuel lines.
It is also recognized that the operational characteristics of the main engine fuel pump vary with different altitude operating conditions. The suction lift capability of a positive displacement pump for drawing fuel to the inlet of the pump (also referred to as net positive suction head) is variable. Performance also varies based upon the vapor-to-liquid ratio of the fuel, with there normally being an increase in vapor relative to liquid at the inlet to the main engine fuel pump as the result of increased altitude.
The use of auxiliary inlets in a positive displacement pump for assuring complete filling of successive pumping chambers to reduce problems encountered by the presence of vapor in the liquid fuel is shown in the Prijatel U.S. Pat. No. 3,182,596.
The use of a jet eductor to collect vapor from the lines of a liquid fuel system and dissolve vapor into the liquid is shown in the Schofield U.S. Pat. No. 3,532,441.